Interpretive Summary: Vinegar is a solution containing acetic acid, an organic acid produced though the natural fermentation of plant materials containing sugars. Vinegar has been identified as a potential organic herbicide, yet more information is needed to determine influence of acetic acid concentration, application volume, and use of additives (adjuvants) on weed control. Acetic acid acts as a contact herbicide, injuring and killing plants by first destroying the cell membranes, which then causes the rapid desiccation of the plant tissues. Household vinegar typically contains 5% acetic acid. Great care must be taken when using acetic acid concentrations of 11% or greater, which can burn the skin and cause serious to severe eye injury, including blindness. Field research was conducted in southeast Oklahoma (Lane, OK) to determine the effect of acetic acid concentrations, application volumes, and adjuvants on weed control efficacy. The factorial experimental design included vinegar at three acetic acid concentrations (0, 5 and 20 %), two sprayer application volumes (20 and 100 gpa), three adjuvants (none, orange oil, and canola oil), and two weedy-checks. Visual weed cover and control ratings were collected 4 days after treatment. The experiment had very high weed densities with multiple species of grass and broadleaf weeds. The average weed cover ratings for the weedy check were as follows: 98% total weeds; 53% grass; 44% broadleaf; 52% large crabgrass (Digitaria sanguinalis (L.)); 25% carpetweed (Mollugo verticillata L.); and 14% cutleaf evening primrose (Oenothera laciniata Hill). Total weed control ranged from 0% control when no vinegar was used to 74% control when 20% acetic acid was applied at 100 gpa with canola oil. Vinegar was more effective in controlling broadleafs than in controlling of grasses. Optimum total grass and crabgrass weed control occurred with 20% acetic acid applied at 100 gpa, resulting in weed control that ranged from 44 to 63%. Broadleaf control was 84% or greater for plots receiving either 10% acetic acid applied at 100 gpa or 20% acetic acid applied at 20 or 100 gpa. Also, 5% percent acetic acid applied at 20 gpa provided good cutleaf evening primrose control (77 to 90%). When averaged across application volumes (20 and 100 gpa) and adjuvants (none, orange oil, and canola oil), weed control increased for all species as acetic acid concentrations increased from 5 to 20%. When averaged across acetic acid concentrations and adjuvants, weed control increased as application volumes increased from 20 to 100 gpa. Individual comparisons among adjuvants within acetic acid concentrations and application volumes showed little or no advantage to adding either orange oil or canola oil to vinegar spray solutions.

Technical Abstract:
Vinegar has been identified as a potential organic herbicide, yet more information is needed to determine influence of acetic acid concentration, application volume, and use of additives (adjuvants) on weed control. Acetic acid acts as a contact herbicide, injuring and killing plants by first destroying the cell membranes, which then causes the rapid desiccation of the plant tissues. Household vinegar typically contains 5% acetic acid. Vinegars with acetic acid concentrations of 11% or greater are available commercially, these produces can burn the skin and cause serious to severe eye injury, including blindness. Field research was conducted in southeast Oklahoma (Lane, OK) to determine the effect of acetic acid concentrations, application volumes, and adjuvants on weed control efficacy. The factorial experimental design included vinegar at three acetic acid concentrations (0, 5 and 20 %), two sprayer application volumes (20 and 100 gpa), three adjuvants (none, orange oil, and canola oil), and two weedy-checks. Visual weed cover and control ratings were collected 4 days after treatment. The experiment had very high weed densities with multiple species of grass and broadleaf weeds. The average weed cover ratings for the weedy check were as follows: 98% total weeds; 53% grass; 44% broadleaf; 52% large crabgrass (Digitaria sanguinalis (L.)); 25% carpetweed (Mollugo verticillata L.); and 14% cutleaf evening primrose (Oenothera laciniata Hill). Total weed control ranged from 0% control when no vinegar was used to 74% control when 20% acetic acid was applied at 100 gpa with canola oil. Vinegar was more effective in controlling broadleafs than in controlling of grasses. Optimum total grass and crabgrass weed control occurred with 20% acetic acid applied at 100 gpa, resulting in weed control that ranged from 44 to 63%. Broadleaf control was 84% or greater for plots receiving either 10% acetic acid applied at 100 gpa or 20% acetic acid applied at 20 or 100 gpa. Also, 5% percent acetic acid applied at 20 gpa provided good cutleaf evening primrose control (77 to 90%). When averaged across application volumes (20 and 100 gpa) and adjuvants (none, orange oil, and canola oil), weed control increased for all species as acetic acid concentrations increased from 5 to 20%. When averaged across acetic acid concentrations and adjuvants, weed control increased as application volumes increased from 20 to 100 gpa. Individual comparisons among adjuvants within acetic acid concentrations and application volumes showed little or no advantage to adding either orange oil or canola oil to vinegar spray solutions.